High School Biology-Chemistry SMILE Meeting
11 February 2003
Notes Prepared by Porter Johnson

Frana Allen [Skinner Elementary School]      Matter and Atoms
passed around several sheets relating to atomic structure. We began by reviewing information on matter [solid-liquid-gas, mass, density, atoms], focusing on the chemical elements:

We then discussed atomic structure, starting with the basic properties of these particles: The complete atom, which contains equal numbers of protons and electrons, is electrically neutral

Frana showed the positions of various elements on the Periodic Table [see the WebElements website: http://www.webelements.com/].   As an example, the element Potassium [found in bananas -- its symbol K comes from its Latin name Kalium] contains P = 19 protons and N = 20 neutrons in its nucleus. Its atomic number Z is equal to the number of protons in the nucleus:  Z = P. Its atomic mass, A = P + N, is given by the total number of protons and neutrons in the nucleus of the atom in question. For Potassium the numbers are Z=20 and A = 39, written as: 19K39.

Frana pointed out that electron orbits are arranged in various types of shells, with each shell holding a certain maximum number of electrons:

Shell Symbol Maximum Number
of  Electrons Allowed
S 2
P 6
D 10
F 14
For Potassium, K, its 19 electrons are arranged in the configuration 1s2 2s2 2p6 3s2 3p6 4s1. That is, there are 2 electrons in the (filled) 1S state, 2 electrons in the (filled) 2S state, 6 electrons in the (filled) 3P state, 6 electrons in the (filled) 2P state, and 1 electron in the (partially filled) 4S state. The chemical properties of atoms depend strongly upon the number of electrons in the partially filled states, and they are called valence electrons. Atoms with the same number of valence electrons in the same type of shell lie in columns in the periodic table, and have similar chemical properties. For example, Hydrogen [1H], Lithium [3Li], Sodium [11Na] from its Latin name, Natrium, Potassium [19K], Rubidium [37Rb], Cesium [55Cs], and Francium [87Fr] lie in the first column of the Periodic Table and form the family of Alkali Metals.

Pat Riley [Lincoln Park HS, Chemistry] pointed out that this simple electronic structure becomes more complicated beyond Z=20 [calcium: Ca], in that D shells begin to contain electrons, and the order of filling electronic shells becomes more complicated.  The filling sequence is as follows:

1S2, 1S2, 2P6, 3S2, 3P6, 4S2, 3D10, 4P 6, 5S2, 4D10, 5P6, 6S2, ...
Beyond that point [Z=56: Barium] one begins to fill the F-shell, which may contain a maximum of 14 electrons.

Using the lovely template distributed by Frana [to see it click here], we determined and studied the structure of the chemical elements for atomic numbers Z= 1 [Hydrogen H] through Z=9 [Fluorine: F].

We learned a lot about atomic structure today.  Nicely done, Frana!

Chris Etapa [Gunsaulus Academy]      Forces and Motion / Cars and Hovercrafts
presented an activity described on the Look · Learn and Do Publications website: http://www.looklearnanddo.comChris successfully used the lesson contained there in her eighth grade class.  First, Chris reviewed the meanings of the terms distance, velocity, and acceleration.  Using boxes equipped with primitive, home-made wheels, the class was divided into groups of 4, and each group designed  and built a car.  Next, the students tested their cars by giving them a push and measuring the distance D traveled over a given time interval T. They then calculated the velocity V = D / T. This completed the activities described on that webpage. 

Next, her students made hovercrafts from one liter water bottles and balloons --- an activity based upon previous SMILE miniteach presentations [ph8901.html; pl95m7.html].  We did a variation of this activity during today's class.

After dividing  into groups of 3-4 participants, we stood the bottle vertically on its base, and cut around the top portion of the bottle at its shoulder, forming an inverted cup-like structure.  We stretched the lip of the balloon over opening of the bottle, with the cap removed, and blew into the opening at the shoulder, inflating the balloon.  When the balloon was inflated we held the air in it by pinching it just above the cup.  We set the apparatus upright on the table, with the shoulder rim resting on the flat surface, and released the pinch.  The air rushed out of the balloon, into the inverted bottle-cup, and out at the shoulder opening or rim, and the hovercraft rose slightly off the table.  In fact, the craft began to move slightly across the table --- presumably because of residual asymmetries. Ken Schug modified the apparatus by taking the  plastic bottle cap, punched a small hole in its center, and then put it on the bottle-cup.  When the balloon was re-attached, re-inflated, and released the outflow of air into the room was reduced, and the motion of the bottle was more stable.  This modification was suggested by Larry Alofs [Kenwood HS, physics], a visitor from the Math-Physics SMILE program.

Great job, as always, Chris!

Fred Schaal [Lane Tech HS, Physics]     Tree Circumferences +  Christmas Bird Survey
described measuring the circumference c (in inches) of  a tree (with roughly circular cross section) in order to determine its diameter d (in inches), by dividing by p » 22/7 (or, better yet, p » 355/113):

d = c / p
Then he raised the question of the potential existence of a fudge factor, ff, which could be multiplied by the diameter to determine the age of a given tree:
age (years) = c (inches) / p ´ ff
One would expect this fudge factor, ff, to be different for each species of tree. In a recent survey of trees at the North Park Village Nature Center [http://www.chicagoparkdistrict.com/parks/North-Park-Village-Nature-Center/] in Chicago, Fred found that the fudge factor, ff, seemed to lie between 3 and 10, depending on the species of tree. Ken Schug asked whether  the fudge factor varies with the age of the tree, or not.  Good question, young man, but we don't yet have an answer.  What do you think?

Fred also reported data on the Christmas Bird Count:

species Percentage of decline
blue jays 60 %
chickadees 35 %
crows 80%
These figures, based upon averages over a ten year period, are believed to be a consequence of the West Nile Virus Epizoötic --- Epidemic of 2002.

You helped us get around a difficult subject which is not just for the birds!  Interesting, Fred.

Scheduled presentations:  Christine Scott [March 09] and Carol Giles [April 08].

Notes taken by Ben Stark.